1. Field of the Invention
The present invention generally relates to a rocker arm assembly. More particularly, the present invention relates to a rocker arm assembly for enabling engine technicians to more quickly and efficiently make valve lash adjustment.
2. Description of the Prior Art
A normal maintenance item for most engines is valve adjustment. Also known as setting “valve clearance” or “valve lash,” this adjustment is an important maintenance item to insure lengthy, proper, and efficient operation of a four stroke engine. The valves in a four stroke engine open and close to allow intake air to flow into and exhaust gases to flow out of the engine. Often times a rocker/follower rides on the cam lobe (with the crankshaft and timing belt/chain turning the cams) and the rocker/follower thus actuates the valves. The cam has a “lump” for lift and a “base circle” for the duration of the engine rotation where the valve is closed. In order to insure that the valves close completely the “valve clearance” or “valve lash” is set so that there is a known clearance between the valves and the rocker arm.
The valve adjustment is important for two reasons. One, if the valves do not close properly, the engine can lose a substantial amount of power since the intake mixture will be “squeezed out” during the compression cycle (hence less mixture burned, less energy resulting from combustion). This might also result in burned valves as the exhaust valves depend partly on contact with the valve seat (head) for cooling. Second, if the valves do not open all the way, the engine will receive poor flow through the head (less mixture) and again lose power.
As the engine ages and more miles are put on it, the valve clearance can change. Repeated thermal cycling of the mechanism as well as mechanical wear will alter the adjustment slightly, resulting (typically) in increased clearance. This increase in clearance is usually characterized by an increased “ticking” at idle. Depending on the motor and the methodology, one may set this adjustment by measuring the clearance between the valve and rocker or the rocker and the cam. It will thus be understood that valve lash adjustment is required with respect to engine rocker arm systems.
Conventional stud mount rocker arm systems are economical to produce but due to the point of claiming, are too flexible and weak. Shaft mount rocker systems provide a rigid mount but with the added expense of necessary pillow blocks. More importantly, the shaft mount system adds reciprocating weight to the end of the rocker arm, reciprocating weight being the enemy of valve train lash.
U.S. Pat. No. 5,645,025 ('025 Patent), which issued to Caya et al., discloses an Internal Combustion Engine. The '025 Patent teaches an internal combustion engine comprising a cast cylinder head having as-cast alignment ribs that align a squared-off fulcrum in a rocker assembly. The rocker arm also has two substantially flat surfaces that engage the planar sides of the fulcrum to minimize lateral movement of the rocker arm. The fulcrum is received between the cast alignment ribs. The ribs are biased from a major axis to insure proper fulcrum alignment during assembly without the use of a jig. More particularly, the '025 Patent teaches a rocker arm having a rocker body that rotates around a trunnion. The trunnion slips over a rocker stud. A nut screws onto the rocker stud to hold the rocker assembly in adjustment. This structural assembly is deficient since the clamping point or bending moment is on the bottom side of the nut, which is a distance away from the head casting.
It will thus be seen from an inspection of the foregoing as well as other teachings commonly known in the art that the prior art does not teach an adjustable rocker arm assembly whereby the rocker stud serves as a fixed mount axis about which an adjustment tower may rotate for adjusting the rocker arm assembly and thus providing valve lash adjustment. The prior art thus perceives a need for an adjustable rocker arm assembly whereby the rocker stud functions as a fixed mount axis about which an adjustment tower may rotate for adjusting the rocker arm assembly, thus providing improved valve lash adjustment